1. Field of the Invention
The present invention relates to solid-state devices and methods of driving the devices.
2. Description of the Related Art
Recently, solid-state image pickup devices including more than millions of pixels have been used for digital cameras, allowing high precision still images to be captured. Also in the case of shooting moving images, it is required that solid-state image pickup devices read out images at high frame rates to enable moving images to be shot without jerkiness. In the case of high-rate reading, since an image accumulation period per frame of photoelectric conversion elements in the pixel portion of a solid-state image pickup device is short, there is a problem in that sufficient exposure amounts are not obtained particularly for dark objects. As means for obtaining sufficient exposure amounts with a limited exposure period, Japanese Patent Laid-Open No. 2006-74440 discloses a method of using two modes of thinning out in a CCD-type image pickup device. According to Japanese Patent Laid-Open No. 2006-74440, one of the two modes is a mode in which fine accumulation period control is performed using an electronic shutter, in a case where the accumulation period is within one vertical scan period. The other mode is a mode in which the accumulation period is fixed without using an electronic shutter, and the amplification factor of signal amplifying means is changed in accordance with the brightness of objects, in a case where the accumulation period exceeds one vertical scan period.
In the solid state image pickup device disclosed in Japanese Patent Laid-Open No. 2006-74440, since switching is performed between two thinning-out reading modes, the method of thinning out changes at the time of switching. In other words, two rows are skipped for every three rows during reading in the case of a shorter accumulation period (for example, 1/30 seconds), whereas only one row is skipped for every three rows during reading in the case of a longer accumulation period (for example, 1/15 seconds). This may be recognizable depending on a shot scene, resulting in discomfort. In addition, in Japanese Patent Laid-Open No. 2006-74440, the amplification factor of a circuit is changed for scenes with accumulation periods of 1/30 to 1/15 seconds. A change in the amplification factor results in a change in the noise of the circuit. Hence, when dark objects are shot in particular, image quality changes at the time of switching between the accumulation periods. This is also recognizable when viewing, resulting in discomfort.